A motorcyclist was fighting for his life yesterday after colliding with a city bus in morning rush-hour traffic, officials said yesterday.

Sources said the unidentified biker sped past a red light at Third Avenue and East 34th Street at 9 a.m. as a traffic agent waved a westbound bus through the intersection. The motorcycle clipped the bus near its back wheel, cops said.

The biker was rushed to Bellevue Hospital, where he was listed in critical condition with severe head trauma and a broken pelvis.